1. Field of the Invention
The present invention relates to a connector for a flat cable for the electric connection between the flat cable and a wiring board.
2. Description of the Related Art
A cable connector has been practically used for the electric connection between electric parts in an electronic equipment. For example, the electric parts are electrically connected to a printed wiring circuit board via a flat cable(FFC) or a flexible printed circuit(FPC). The cable connector being in practical use includes a rotary type and a sliding type, for example, which are different from each other in the method for fixing the cable.
As shown in FIGS. 16A and 16B, the sliding type cable connector includes a connector body 18 disposed on a printed wiring board 2 and having a cable accommodation portion 16, a plurality of contact terminals 20ai (wherein i=1 to n; n is a positive integer) provided in the cable accommodation portion 16 of the connector body 18, for electrically connecting an electrode section of the printed wiring board 2 with a terminal section 6E of a flexible printed circuit 6, and a stopper member 22 supported to be slidable relative to the connector body 18.
The connector body 18 is provided at one end thereof with an inserting opening 24 for allowing the terminal section 6E of the flexible printed circuit 6 to be connected to pass through the same. The inserting opening 24 is communicated with the cable accommodation portion 16 formed in the interior of the connector body 18. The cable accommodation portion 16 in the connector body 18 is defined by the inner wall of the connector body 18 encircling the same. A guide groove 18g is provided in the inner wall of a portion of the cable accommodation portion 16 forming the upper region thereof, for supporting opposite ends of the stopper member 22 to be slidable along the same, and extends in the direction for the attachment/detachment of the flexible printed circuit 6. The stopper member 22 is operated when a movable terminal portion of the contact terminal 20ai is attached to or detached from the terminal section 6E of the flexible printed circuit 6 and the stopper member 22 has a pressing-surface 22a in a region opposed to the movable terminal portion of the contact terminal 20ai. The pressing surface 22a presses a back plate 6B of the flexible printed circuit 6 toward the movable terminal portion of the contact terminal 20ai described later, while sliding along the back plate 6B.
A guide surface 22b having a slant 22s is formed in a middle portion of a surface of the stopper member 22 opposite to the pressing surface 22a. 
The plurality of contact terminals 20ai are arranged in the cable accommodation portion 16 in correspondence with the arrangement of the terminal section 6E of the flexible printed circuit 6. The respective contact terminal 20ai is comprised of a fixed terminal portion 20S soldered to the terminal section of the printed wiring board 2, a guide piece 20B, a movable terminal portion 20A bifurcated therefrom, and a coupling section 20C for connecting the fixed terminal portion 20S to a joint at the confluence of the guide piece 20B and the movable terminal portion 20A.
A tip end of the guide piece 20B of the respective contact terminal 20ai is positioned to face to the guide surface 22b of the stopper member 22. The movable terminal portion 20A has a contact portion at a tip end thereof to be electrically connected to the terminal section 6E of the flexible printed circuit 6.
The coupling section 20C is fixed to the connector body 18 by press-fitting a projection thereof into a slit formed adjacent to the cable accommodation portion 16 of the connector body 18.
Thus, when the slant 22s of the stopper member 22 is away from the cable accommodation portion 16 and the guide piece 20B; that is, in an unlocked state as shown in FIG. 16A, the slant 22s of the guide piece 20B is away from the guide piece 20B to result in a non-engaged state relative to the guide piece 20B. Accordingly, it is possible to insert the terminal section 6E of the flexible printed circuit 6 into the cable accommodation portion 16 through the inserting opening 24.
In this structure, during the electric connection of the terminal section 6E of the flexible printed circuit 6 with the contact portion of the respective contact terminal 20ai, after the terminal section 6E of the flexible printed circuit 6 has been inserted to a position in the vicinity of a rear wall 18a defining a rear side of the cable accommodation portion 16 in the direction shown by an arrow F through the inserting opening 24 when the slant 22s of the stopper member 22 is away from the cable accommodation portion 16, a tip end of the stopper member 22 is made to slide in the direction shown by an arrow L. Thus, the terminal section 6E of the flexible printed circuit 6 is pressed onto the contact portion of the movable terminal portion 20A of the contact terminal 20ai by the pressing surface 22a of the stopper member 22 to result in the electric connection.
At that time, the terminal section 6E of the flexible printed circuit 6 is nipped between the pressing surface 22a of the stopper member 22 and the elastically deformed movable terminal portion 20A of respective contact terminal 20ai and maintained there by the mutual frictional force.
In the above-mentioned cable connector, when a signal in a relatively high frequency band is transmitted, the impedance matching between the electronic equipment and the connector is proposed as a countermeasure for restricting a cross-talk or a reflection of signal that is considered to be a cause of the distortion of waveform.
Also, it has been known that the signal transmission performance in a relatively high frequency band is enhanced in the cable connector by reducing the inductance by shortening a length L between the contact portion and the proximal end of the movable terminal portion 20A of the contact terminal 20ai shown in FIG. 16A, together with the impedance matching.
When the length L is shortened between the contact portion and the proximal end of the movable terminal portion 20A of the contact terminal 20ai as described above to reduce the inductance, it is necessary to change a spring constant of the movable terminal portion 20A.
For example, when the movable terminal portions 20A different in spring constant each other are elastically deformed, the relationship between a displacement δ in the contact portion and a load P applied to the contact portion is represented by straight lines La and Lb as shown in FIG. 17. In FIG. 17, the vertical axis and the horizontal axis represent the load P and the displacement δ, respectively, so that the change in load P that acts on the contact portion is illustrated in correspondence to the displacement δ of the contact portion.
When the spring constant of the movable terminal portions 20A different each other, the straight lines La and Lb illustrate that the gradient of the straight line La describing the spring constant is smaller than the that of straight line Lb. Accordingly, in an allowable the load P range from Pa to Pb (for example, from 30 g to 50 g), as the range should not be changed even if the length L is shortened to increase the spring constant, thus, an allowable the displacement δ range of the contact portion is changed from a range from δ3 to δ4 (δA); for example, from 0.2 to 0.3 mm; in accordance with the straight line La to a smaller and narrower range from δ1 to δ2 (δB) in accordance with the straight line Lb.
However, when the stopper member 22 is injection-molded and the contact terminal 20ai is manufactured by the press, as suppressing the variance of the manufacturing accuracy of the parts has a fixed limit, it may be difficult to coincide the above-mentioned displacement width of the contact portion with the allowable range (δB) from δ1 to δ2 in accordance with the straight line Lb.